334 APPLIED ENTOMOLOGY 



host animal. Rows of stout spines may be present on the head just 

 above the mouth or on the pronotum or in both places. These are called 

 tsenidia and are useful in identifying the species. The legs are long 

 and powerful. Wings are absent but flat scales present on the meso- 

 and metathorax are generally regarded as their rudiments. The larvae 

 are worm-like, with chewing mouth parts and pupate within a cocoon. 



The characters distinguishing these insects are: 



Insects which as adults have their bodies strongly compressed sideways; 

 are without wings and compound eyes but have legs. Mouth parts for pierc- 

 ing and sucking. Larvce worm-like. Metamorphosis complete. 



Adult fleas feed entirely upon the blood of mammals and birds, 

 but while each species has what may be termed its preferred host, there 

 seems to be some latitude in this, and other animals may also be attacked. 



The eggs are laid loosely among the hairs of the host and drop to 

 the ground where they hatch. The larvae which are slender, whitish, 

 and rather worm-like, with chewing mouth parts, feed on decaying vege- 

 table and animal matter for a period varying from a few days to several 

 months. When feeding is completed, the larva spins a silken cocoon in 

 which it pupates. Here it may remain only a few days or for a time 

 which may be more than a year, according to circumstances, before 

 emerging as the adult. The adults in hot weather and with no food will 

 live only a few days but when food is available they may live a month 

 or even nearly a year. Winter in the North is usually spent in one or 

 another of the early stages, but in the South the adults may be present 

 on their hosts at any time. 



Hot, dry weather is not favorable to the rapid breeding of these 

 insects but, in damp, rainy weather, they increase rapidly, particularly 

 in sandy localities as the moisture there is more uniform where the early 

 stages live, though too much moisture is injurious to them. 



Fleas are mainly household pests, coming in on cats and dogs, the cat 

 flea being the most common generally, though in the West and South 

 the human flea is also abundant. The eggs dropped by the fleas fall to 

 the floors and the larvae feed on any material found under rugs and mat- 

 tings, in floor cracks and similar places, and, on reaching maturity, attack 

 the fir"st animal they can reach. 



Various animals besides those already mentioned serve as hosts. 

 Among them are hogs, poultry and other birds. Horses, cattle and 

 sheep are not often attacked. 



Fleas have become of importance to man aside from their attacks on 

 his person with the discovery that they may carry the germs of the 

 bubonic plague. This much dreaded disease with its high mortality 

 caused by Bacillus pestis occurs in rats' blood, and by feeding on this 

 the flea brings the germs into its own body. When a flea attacks a 

 person, it often ejects partly digested blood and also feces near the 



